ABSTRACT: BACKGROUND: Classic, long duration aerobic exercise reduces cardiovascular and metabolic disease risk but this involves a substantial time commitment. Extremely low volume high-intensity interval training (HIT) has recently been shown to cause similar improvements to aerobic performance, but it has not been established whether HIT has the capacity to improve glycemic control. METHODS: Sixteen young men (age: 21+/-2 y; BMI: 23.7+/-3.1 kg * m-2; VO2peak: 48+/-9 ml * kg-1 * min-1) performed 2 weeks of supervised HIT comprising of a total of 15 min of exercise (6 sessions; 4-6 x 30-s cycle sprints per session). Aerobic performance (250-kJ self-paced cycling time trial), and glucose, insulin and NEFA responses to a 75-g oral glucose load (oral glucose tolerance test; OGTT) were determined before and after training. RESULTS: Following 2 weeks of HIT, the area under the plasma glucose, insulin and NEFA concentration-time curves were all reduced (12%, 37%, 26% respectively, all P<0.001). Fasting plasma insulin and glucose concentrations remained unchanged, but there was a trend towards reduced fasting plasma NEFA concentrations post-training (pre: 350 +/- 36 v post: 290 +/- 39 mumol * l-1, P=0.058). Insulin sensitivity as measured by the Cederholm index was improved by 22.5% (P<0.01). Aerobic cycling performance was improved by ~6% (P<0.01). CONCLUSIONS: The efficacy of a high intensity exercise protocol, involving only ~250 kcal work each week, to substantially improve insulin action in young sedentary subjects is remarkable. We feel this novel time-efficient training paradigm can be used as a strategy to reduce metabolic risk factors in young and middle aged sedentary populations who otherwise would not adhere to a classic high volume, time consuming exercise regimes.